1. Field of the Invention
The present invention relates to a driving device and method for a plasma display panel (PDP), and more particularly, to a PDD including a driving device and using a driving method to recover a data voltage drop component occurring in an address discharge.
2. Description of the Background Art
Plasma display panel (PDP) displays a picture including a character or a graphic by exciting a phosphor using an ultraviolet ray of 147 nm, which is generated when an inert mixture gas such as He+Xe, Ne+Xe, or He+Ne+Xe is discharged.
FIG. 1 is a view illustrating a three-electrode alternate current surface discharge type PDP according to the background art. Referring to FIG. 1, the three-electrode alternate current surface discharge type PDP includes a scan/sustain electrode 11a and a common sustain electrode 12a formed on an upper substrate 10, and an address electrode 22 formed on a lower substrate 20. Each of the scan/sustain electrode 11a and the common sustain electrode 12a is formed of a transparent material, for example, of indium-tin-oxide (ITO). Metal bus electrodes 11b and 12b are formed at each of the scan/sustain electrode 11a and the common sustain electrode 12a to reduce resistance. An upper dielectric layer 13a and a protective film 14 are layered on the upper substrate 10 having the scan/sustain electrode 11a and the common sustain electrode 12a formed thereon. Wall charges are generated in plasma discharge and accumulated on the upper dielectric layer 13a. The protective film 14 prevents the upper dielectric layer 13a from being damaged by sputtering generated in the plasma discharge, and increases a secondary electron emission efficiency. In general, the protective film 14 is formed of magnesium oxide (MgO).
Meantime, a lower dielectric layer 13b and a barrier rib 21 are formed on the lower substrate 20 having the address electrode 22 formed thereon. A phosphor layer 23 is coated on surfaces of the lower dielectric layer 13b and the barrier rib 21. The address electrode 22 is formed in a direction of intersecting with the scan/sustain electrode 11a and the common sustain electrode 12a. The barrier rib 21 is formed in parallel with the address electrode 22, thereby preventing ultraviolet ray and visible ray, which are generated in the plasma discharge, from being leaked to an adjacent discharge cell. The phosphor layer 23 is excited by the ultraviolet ray to generate any one of red, green and blue visible light. The inert mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe is injected into a discharge space of the discharge cell for discharge. The discharge space is provided between the upper and lower substrates 10 and 20 and the barrier rib 21. A method of expressing an image grayscale of the above-constructed PDP will be described with reference to FIG. 2.
FIG. 2 illustrates the method of expressing the image scale of the PDP of FIG. 1.
As shown in FIG. 2, the image grayscale is expressed with one frame divided into various sub-fields each sub-field having different light emission times. Each of the sub-fields is divided into a reset period for uniformly generating discharge, an address period for selecting the discharge cell, and a sustain period for embodying the grayscale depending on discharge times. For example, in case where an image is displayed in 256 grayscales, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight sub-fields. Each of the eight sub-fields is again divided into a reset period, an address period and a sustain period. The reset period and the address period are the same a each sub-field, whereas the sustain period is increased in the ratio of 2n (n=0, 1, 2, 3, 4, 5, 6, 7) at each sub-field. This increase in the sustain period is fixed and implemented automatically independent of any signal/voltage characteristics of the PDP. A driving waveform of the PDP driven with the divided sub-fields will be described as follows referring to FIG. 3.
FIG. 3 illustrates the waveform for describing the driving method for the PDP according to the background art. Referring to FIG. 3, the PDP is driven by dividing a sub-field into an initialization/reset period for initializing an entire picture, an address period for selecting a cell, and a sustain period for sustaining a discharge of the selected cell.
At a setup period (SU) of the initialization period, a ramp-up waveform (Ramp-up) is concurrently supplied to all scan electrodes (Y). The ramp-up waveform causes the discharge in cells of the entire picture. By the setup discharge, positive (+) wall charges are accumulated on the address electrode (X) and the sustain electrode (Z), and negative (−) wall charges are accumulated on the scan electrode (Y). After the supplying of the ramp-up waveform, a ramp-down waveform (Ramp-down) is supplied at a setdown period (SD) to generate a weak erasure discharge, thereby partially erasing excessive wall charges. The ramp-down waveform begins to drop from a positive voltage lower than the peak voltage of the ramp-up waveform to a ground voltage (GND) or a specific positive voltage level. By the setdown discharge, the wall charges are uniformly remained within the cells to stably generate an address discharge.
At the address period, a negative scan pulse (scan) is sequentially supplied to the scan electrodes (Y) and at the same time, a positive data pulse (data) is supplied to the address electrodes (X) in synchronization with the scan pulse (scan). While a voltage difference between the scan pulse and the data pulse is summed with a wall voltage generated during the initialization period, the address discharge is generated within the cell to which the data pulse (Dp) is supplied. The wall charges are formed within the cells selected by the address discharge to generate the discharge at the time of applying a sustain voltage. A positive direct current voltage (Zdc) is supplied to the sustain electrode (Z) to reduce a voltage difference between the sustain electrode (Z) and the scan electrode (Y) at the setdown period and the address period. By doing so, an erroneous discharge is prevented between the sustain electrode (Z) and the scan electrode (Y).
In the sustain period, a sustain pulse (sus) is supplied alternately to the scan electrodes (Y) and the sustain electrodes (Z). While the wall voltage of the cell is summed with the sustain pulse (sus), a sustain discharge (that is, a display discharge) is generated between the scan electrode (Y) and the sustain electrode (Z) at the cell, which is selected through the address discharge, whenever the sustain pulse (sus) is supplied.
After the completion of the sustain discharge, a ramp waveform (erase) having a small pulse width and voltage level is supplied to the sustain electrode (Z) to erase the wall charges remaining within the cells of the entire picture.
Meantime, in the PDP driven in the above method, when the positive data pulse (data) is applied to the address/data electrodes (X) and synchronized to the scan pulse at the address period, thereby discharging the cell, a voltage of the data pulse (i.e., the level of the data voltage Vd supplied to a data electrode X as the data pulse) drops depending on a discharge pattern of the discharge cell. This is because a switching load of the data electrode X is increased due to the large switching time at the data electrode depending on the discharge pattern of the discharge cell as shown in FIGS. 4a-5b. The discharge pattern means a pattern of data or a data pattern established by 0's and 1's. The switching time refers to a number of switchings from 0 to 1 or 1 to 0 within the data supplied to the data electrodes.
FIGS. 4a-5b illustrate data voltage characteristics depending on the discharge pattern of the discharge cell of a PDP according to the background art. In other words, FIGS. 4a and 4b illustrate the data voltage (Vd) characteristic at the address period when the discharge cell belonging to one line (e.g., X1) of the data electrode is continuously discharged, that is, when switching times for supplying the data pulse Dp (Data) are small. FIGS. 5a and 5b illustrate the data voltage (Vd) characteristic at the address period when the discharge cell belonging to one line (e.g., X1) of the data electrode is noncontinuously and irregularly discharged, that is, when the switching times for supplying the data pulse Dp to the line X1 are large.
In case where the PDP has the discharge cell pattern having the small switching times for supplying the data pulses as shown in FIG. 4a, the data voltage (Vd) supplied to the data electrode X1 may drop slightly during the address period as shown in FIG. 4b. On the contrary, in case where the PDP has the discharge cell pattern having the large switching times for supplying the data pulse as shown in FIG. 5a, the voltage (Vd) supplied to the data electrode heavily drops during the address period as shown in FIG. 5b. This creates a drawback in that the erroneous discharge is generated due to the jittering such as a case where the address discharge is not sufficiently generated only with an exterior predetermined data voltage at the address period of the next sub-field since the drop of the data voltage is not sufficiently recovered during the sustain period.
In particular, this drawback is more prominent in the PDP using a single scan method. In the PDP using the single scan method, the switching load increases due to a longer line length of the data electrodes, which in turn causes an increase in the amount of data voltage drop for the data electrodes. Also there is a drawback in that when the PDP is driven at a high temperature, the erroneous discharge is easily caused due to the loss of the wall charge, because a motion of a spatial charge is activated within the cell and a recombination is easily generated.